1. Field of the Invention
The present invention relates generally to a reclining seat having a seat cushion and a seat back pivotally mounted on the seat cushion and, in particular but not exclusively, to a locking structure for the reclining seat to lock the seat back relative to the seat cushion.
2. Description of the Related Art
Japanese Laid-Open Patent Publication (unexamined) No. 8-214978 discloses a reclining structure for use in a reclining seat. This reclining structure includes a lower arm mounted on a rear end of a seat cushion, an upper arm mounted on a lower end of a seat back, an internally-toothed gear formed on the upper arm, a pair of protruding portions formed on the lower arm and placed inside the internally toothed gear, two guide grooves defined between the pair of protruding portions, and a pair of pawls received in the two guide grooves, respectively, so as to be movable in opposite directions.
The pair of pawls are placed symmetrically with respect to an operation shaft connected to an operation lever. Upon operation of the operation lever, the pair of pawls are moved between a locked position where the pawls engage with the internally-toothed gear and an unlocked position where the pawls disengage from the internally-toothed gear. When the pawls are held at the locked position, rotation of the seat back about the operation shaft is prevented, thereby maintaining the posture of the seat back relative to the seat cushion. In contrast, when the pawls are held at the unlocked position, the angle of inclination of the seat back relative to the seat cushion can be changed by rotating the seat back about the operation shaft.
Recently, the locking structure tends to be made compact, followed by miniaturization of its component parts. However, if the size of the pawls is reduced, the area of contact between the pawls and the pair of protruding portions is reduced. As a result, the pawls cannot be positively supported by the protruding portions and readily chatter within the guide grooves, thus making it impossible to stably maintain the posture of the seat back and lowering the comfort of sitting on the seat.
Furthermore, it is likely that a "biased action" will occur in which only one of the pawls is held in mesh with the internally-toothed gear due to manufacturing errors, making it difficult to set the seat back at a desired angle of inclination.